发布于 2015-08-16 14:47:33 | 88 次阅读 | 评论: 0 | 来源: 网络整理
运算符优先级决定的条款在表达式中的分组。这会影响一个表达式如何计算。某些运算符的优先级高于其他;例如，乘法运算符的优先级比加法运算符高。
例如X =7 +3* 2; 这里，x被赋值13，而不是20，因为运算符*的优先级高于+，所以它首先被乘以3 * 2，然后再加上7。
这里，具有最高优先级的操作出现在表的顶部，那些具有最低出现在底部。在表达式中，优先级较高的运算符将首先计算。
| 分类 | Operator | 关联 |
|---|---|---|
| Postfix | () [] -> . ++ - - | Left to right |
| Unary | + - ! ~ ++ - - (type)* & sizeof | Right to left |
| Multiplicative | * / % | Left to right |
| Additive | + - | Left to right |
| Shift | << >> | Left to right |
| Relational | < <= > >= | Left to right |
| Equality | == != | Left to right |
| Bitwise AND | & | Left to right |
| Bitwise XOR | ^ | Left to right |
| Bitwise OR | | | Left to right |
| Logical AND | && | Left to right |
| Logical OR | || | Left to right |
| Conditional | ?: | Right to left |
| Assignment | = += -= *= /= %=>>= <<= &= ^= |= | Right to left |
| Comma | , | Left to right |
试试下面的例子就明白了在D编程语言中的运算符优先级可供选择：
import std.stdio;
int main(string[] args)
{
int a = 20;
int b = 10;
int c = 15;
int d = 5;
int e;
e = (a + b) * c / d; // ( 30 * 15 ) / 5
writefln("Value of (a + b) * c / d is : %dn", e );
e = ((a + b) * c) / d; // (30 * 15 ) / 5
writefln("Value of ((a + b) * c) / d is : %dn" , e );
e = (a + b) * (c / d); // (30) * (15/5)
writefln("Value of (a + b) * (c / d) is : %dn", e );
e = a + (b * c) / d; // 20 + (150/5)
writefln("Value of a + (b * c) / d is : %dn" , e );
return 0;
}
当编译并执行上面的程序它会产生以下结果：
Value of (a + b) * c / d is : 90
Value of ((a + b) * c) / d is : 90
Value of (a + b) * (c / d) is : 90
Value of a + (b * c) / d is : 50